Relationship Between Bone Mineral Density and Periodontitis Periodontal disease and osteoporosis effect millions of people in the United States and the world. Both diseases lead to a significant amount of morbidity, mortality, and expenses. The relationship between these two diseases still remains indefinite. The limited literature on this field fails to provide a convincing conclusion due to flaws in either the design or statistical analysis such as small sample sizes, inadequate control of confounding and bias, different study populations, varying methods or sites used to assess periodontal disease or osteopenia. The specific aims of this study are to determine if systemic and mandibular bone loss are associated with increased prevalence and severity of periodontitis with a cross-sectional design, and to determine which risk indicators identified in the cross-sectional study are associated with incidence and progression of periodontitis through a follow-up examination with a prospective design. The study population will consist of postmenopausal women, will come from the Women's Health Initiative observational component, and it is estimated that about 1,300 will be eligible for this study. Up today we have examined 208 subjects. The dependent variable, periodontal disease severity is represented by clinical attachment level, and computer assisted radiographic measurement of interproximal alveolar bone loss. Other measures of periodontal status also includes probing pocket depth, supragingival plaque, gingival bleeding on probing, calculus, and number of remaing teeth. Skeletal osteopenia is assessed by a dual x-ray absorptiometer, which measures bone mineral density, at the premolar and molar regions of the mandible; the neck, trochanter, intertrochanter, Ward's triangle and total regions of the femur, and from anterior-posterior and lateral views of the lumbar spine. Examinations have been performed by calibrated blind examiners, and their reproducibility will be assessed throughout the study period. Key words: Osteoporosis, bone mineral density, periodontal disease.